The textiles industry uses synthetic fibers for a wide variety of applications including clothing and other fabric items which are desirably manufactured and marketed in a variety of colors and patterns. In many circumstances, the synthetic fibers are white or natural in color; therefore, manufacturing techniques are required to add color to synthetic fibers.
As known to those familiar with the textile arts, various techniques are used to obtain the desired color in various textile products. Typically, conventional techniques include adding liquid colorant to the basic structures of textile products. These basic structures include fibers, yams made from fibers, and fabrics made from yarns. The various techniques for coloring include dying individual fibers before they are formed into yams, dying yarns before they are formed into fabrics, and dying woven or knitted fabrics.
Although the term "dye" is often used in a generic sense, those familiar with textile processes will recognize that the term "dye" most properly describes a colorant that is soluble in the material being colored. In comparison, the term "pigment" should be used to describe insoluble colorants.
Many conventional techniques for coloring synthetic filaments include the incorporation of dye into the polymer material after the filament has been extruded.
Another conventional method in the textiles industry for coloring synthetic filaments includes the "master batch" approach in which colorant is dispersed at a relatively highly concentrated level into a small sample of polymer chip. The highly concentrated colored chip polymer is introduced to the melt spinning system, blended with a larger volume of colorless virgin polymer chip and then extruded to hopefully achieve filaments with the desired color throughout the melt-spinning process. The processes associated with the master batch approach, however, can be expensive and time consuming. For example, the amount of solid dyestuffs introduced into the master batch must be precisely monitored in order to maintain a consistent color. Furthermore, it is extremely difficult to obtain a precise shade or variant of a particular color. Oftentimes it is necessary to re-extrude the polymer to obtain a required color specification of the master batch chip.
Because the masterbatch process typically uses solid dyestuffs, it raises difficulties in accurately handling the proper amounts of solids. Solids are generally harder to meter in precise amounts than are liquids or gases, harder to mix uniformly with other materials, and harder to handle as supply streams (several of which are typically required).
Furthermore, a typical masterbatch process requires multiple high-temperature process steps (i.e., compounding the dyestuff and polymer; drying the compounded mixture; and recompounding the master batch with the full polymer supply) which, both individually and collectively, can cause varying color results or even degradation of the polymer itself.
Condensation polymers offer additional challenges to the masterbatch system. As is known to those familiar with chemical reactions. a condensation polymer results from a reaction in which two monomers or oligomers react to form a polymer and a water molecule. Because such reactions produce water, they are referred to as "condensation" reactions. Because of chemical equilibrium, however, the water must be continually removed from the polycondensation reaction, otherwise it tends to drive the reaction in the other direction; i.e., depolymerize the polymer. This results in a loss of molecular weight in the polymer which is referred to as hydrolytic degradation. In particular the molecular weight (measured by the intrinsic viscosity or "IV") of polyester can easily be decreased by as much as 0.15 dl/g (0.55-0.75 dl/g is considered a good viscosity for filament). As a greater problem--and one that becomes evident during later processing of filament and yarn--the loss in IV is quite variable depending upon the quality of process control of the masterbatch drying and extrusion systems. In particular, obtaining the required color specification of the masterbatch chip sometimes requires re-extruding the polymer to obtain a desired color correction. Unfortunately, such re-extrusion for color matching purposes tends to increase the loss in molecular weight even further.
Masterbatch "chip" is generally introduced into the spinning process using several options each of which tends to provide an extra source of variation for the resulting molecular weight. Because there are several process steps during which molecular weight can be lost, the effect tends to be cumulative and significant. The overall effect is a significant reduction in the molecular weight of the filament that manifests itself as an orientation variability in the resulting yarn. In turn, the orientation variability produces a resulting variability in the physical properties of the yarn such as elongation, tenacity, and draw force.
Such variability in the physical properties of spun yarn generates several additional problems. For example, partially oriented yarn (POY) which is draw textured must exhibit uniform draw force to assure that its preaggregate tension stays within desired specifications. If the yarn properties are outside of such specifications, various problems such as twist surging occur and prevent processing the yarn at commercial speeds. Furthermore, the drawing performance of spun yarns, whether POY, low orientation yarns (LOY), fully oriented yarns (FOY), or staple, is highly dependent upon consistent elongation because the imposed draw ratio cannot exceed the inherent drawability of the spun yarn (as measured by the elongation). Additionally, consistent physical properties of the final drawn or draw textured filament are desirable for optimum performance of fabrics and other end-use products.
In a practical sense, the variation in physical properties from filament to filament, fiber to fiber, and yarn to yarn forces the various textile manufacturing processes and machinery to be continually readjusted whenever a new colored fiber or yarn is introduced. Thus, the problems inherent in masterbatch coloring tend to raise the cost and lower the productivity of later textile processes that incorporate masterbatch colored fibers and yarns.
Copending and commonly assigned application Ser. No. 08/929,831 discloses a particular technique for delivering liquid colorants into the base chip before the chip is melted and includes the use of an injector structure. The liquid colorant can be injected into an extruder or at a point just prior to a manifold system, dependent upon the placement of the injector. The liquid colorants are slowly fed into the base chip in small amounts because the colorant is highly concentrated. In this fashion, the operator is able to better control the amount of liquid colorant deposited into the base chip and, therefore, obtain the desired color during a first attempt. In certain circumstances, however, the slow-feed technique can result in the organic colorants remaining in the bore of the injector for prolonged periods of time. Consequently, the colorant may "cook" (degrade) or solidify due to the heat transfer from the extruder--which is normally heated in order to melt the polymer--to the injector structure.
The solid degradation product resulting from the prolonged heating of the colorant plugs or clogs the bore of the injector and prevents the delivery of the liquid colorant. Thus, when the injector becomes clogged, the operator must halt the production line, locate the clogged injector, and detach the injector from the machinery. Next, the operator must clear the obstruction (i.e., globule of solid dye) from the bore of the injector with specialized tools and then reattach the cleansed injector onto the machinery before resuming normal operations.
Alternatively, an operator could simply replace the defective or clogged injector with a properly functioning injector and immediately resume operations. The defective injector could then be subsequently cleaned during a routine maintenance interval. Regardless of the alternative chosen by an operator to remedy the clogged bore, the defective injector must be physically removed from the production line. Thus, the use of conventional injectors requires additional downtime to clean clogged injectors. Accordingly, there is a need for an injector structure comprising a self-cleaning means for clearing a clogged bore. Such an injector structure would allow an operator to clear the path of the clogged bore without having to remove the entire structure from the melt-spinning machinery.
As referenced above, conventional techniques of coloring textile filaments include positioning an injector adjacent to the extruder. This placement results in the heating and subsequent solidification of the liquid colorant. Accordingly, there is also a need for a cooling means in an injector to reduce the amount of heat transferred from the extruder to the injector structure.